Monday, June 14, 2010

Sahul’s climate changed dramatically during the period of the last glacial maximal, between 22,000 BP and 17,000 BP. Average temperatures were quite a bit lower than previously, and dry winds made those temperatures feel even colder. Evaporation rates were higher than either today or in the previous period, and rainfall is estimated to have been about half of what it is today (Hiscock 2008, 58). This period was exceptionally difficult for humans in Sahul due to loss of food sources through extinctions, lack of water, and the cold. As a result of these changes, many pre-LGM settlements show no activity at all during this period; some of these sites are at Lake Eyre and the Strzelecki and Great Sandy deserts (Hiscock 2008, 60). These sites were probably so dry that even underground and other previously reliable water sources dried up and thus could not support life; another theory is that the areas around these sites became so dry that it was impossible for large groups to carry enough water with them to migrate into them.

Another feature of Sahul during the LGM was the final extinction of a large group of animals referred to as megafauna, including 10-foot-tall kangaroos and diprotodontids, which looked most like contemporary rhinoceroses but were marsupials rather than placental mammals. The cause of this extinction remains a contentious issue today with some scientists, such as Tim Flannery (1994, 2004), claiming a direct link between this mass extinction and the Aboriginal population’s hunting or land-use schemes, and others favoring a direct link between climate change and extinction. Stan Florek (2003) of the Australian Museum in Sydney is a proponent of the latter theory, who argues that temperature changes without any significant rise in moisture levels contributed to the drying out of the continent’s inland lakes and thus the death of the animals that relied on their water. Peter Hiscock (2008, 72–75) likewise draws on evidence from a variety of archaeologists, especially Judith Field’s work at Cuddie Springs, to argue for climate change as the source of not only LGM extinctions but also those of many other large marsupials between 200,000 BP and the LGM. Along with Hiscock, the present author cannot rule out that humans may have assisted in the extinction of some animals through either hunting or disrupting their natural habitats, but it seems clear that the earliest Aboriginal populations did not kill off Sahul’s megafauna.

After the end of the last glacial maximal about 17,000 years ago, conditions in Sahul began to change. These changes were not rapid by contemporary standards but over the course of thousands of years did force the human population on Sahul to make many significant adaptations. The most important cause of these changes was the rise in global sea levels, which over the course of 10,000 years eventually separated the Australian mainland from Tasmania and New Guinea. In addition to the loss of territory, climate change affected the continent in ways that are still not understood. Warmer conditions and an increase in carbon dioxide (CO2) in the atmosphere may have set the stage for more plant life. Greater rainfall may have opened up certain desert locations that had been abandoned during the LGM, while warmer temperatures may have caused this additional moisture to evaporate as soon as it fell.

While domestication of animals and plants was largely impossible in the Australian context because of a lack of suitable native species (Diamond 1999), post-LGM archaeological sites indicate other, significant changes in both social and material life for humans on the continent. Socially, the decrease in available territory caused by inundation contributed to higher population densities. This fundamental change, however, does not seem to have brought about any categorical change in social structure. Post-LGM Aboriginal societies remained bands, organized around the dual principles of kinship and residence and exhibiting all of the relative equality of their pre-LGM ancestors. Even in New Guinea, where population pressures about 9,000 years ago contributed to the domestication of plants and the development of a horticultural subsistence base, extensive redistribution systems eliminated differences in wealth almost as soon as they emerged and no formal leadership roles developed prior to the colonial era. The same was certainly true in Australia, where horticulture could not develop, making it impossible to accumulate large food surpluses.

The combination of higher population densities and climate change also caused many material changes to post-LGM Aboriginal life, especially the need for more intensive utilization of resources in each locality. For example, many of the chert tools and fragments found in pre-LGM and LGM era middens had been carried far from their original sources. For many archaeologists, this indicates greater mobility at that time due to the requirements of hunting and gathering in the cold, dry climate. This mobility also points to the ability of each band to roam far and wide without encroaching on the territory of other bands. In some post-LGM sites, most chert remains are found quite close to their source and thus indicate longer residence in each place and reduced mobility due to an increase in overall population (O’Connell and Allen 2004). However, these conclusions have been challenged by findings that some large stone tools, such as axes, were discovered farther from their original sites during the pre- and post-LGM periods than during that period, when dryness and cold may have prevented some migratory routes and camping sites from being used. Many post-LGM sites also indicate that trade relations increased in that period and thus gave each band access to a somewhat wider array of goods without their being forced to migrate.

Another important material change in the post-LGM context was the widespread creation of art and body decorations. Very few pre- LGM sites indicate the presence of red or yellow ochre or any other artistic media. All of the rock art for which Aboriginal Australians are famous, such as X-ray art of animals and dot paintings showing song lines and the footsteps of the ancestors, was created in the post-LGM period. Whether this material change is indicative of greater complexity in Aboriginal religious and ritual life at this time or another result of higher population densities and reduced mobility may never be known. A further possibility is that all pre-LGM rock art was destroyed by inundation or simply eroded over time. The fact that there are two possible examples of pre-LGM rock art in the Cape York Peninsula area of northern Australia in the form of ochre smudges on rock overhangs may provide evidence for this theory.

X-ray painting and dot painting are the two best-known forms of traditional Aboriginal art. This example comes from the Kakadu region of the Northern Territory. (Neale/Shutterstock)

After the LGM, Aboriginal people also began to make more widespread changes to their natural environment than they had prior to and during the LGM. The use of fire is one land management strategy that may have been practiced prior to the LGM but nonetheless became very widespread after it, as seen at a large number of post-LGM archaeological sites. As do contemporary Aboriginal people, these ancient ancestors may have used fire to locate and isolate animals for easier hunting as well as to promote the growth of vegetation, which would also have attracted animals. In addition to the use of fire to control plant growth, there is evidence that both plants and small animals were carried from place to place to encourage their growth in new habitats. Lack of suitable candidates for domestication, such as those that could have provided enough food effectively to replace hunting and gathering, however, meant that domestication of these plants never occurred. Indeed, even in the postcolonial context, the only native Australian plant to have been domesticated for widespread human consumption is the macadamia nut, and no native animal has been domesticated (Diamond 1999).

As have other aspects of the most ancient Aboriginal history, this hypothesis concerning greater control of the natural environment in the post-LGM period has been challenged. For example, some prehistorians have used evidence of heavily used stone axes in a few pre-LGM sites, combined with pollen studies indicating greater forest cover in central Australia prior to 60,000 BP, to argue that the first migrants to the country cut down large swaths of forest in that region. The argument is that the resulting lack of trees contributed to desertification, indicating very intensive interactions between pre-LGM populations and their environment (Groube 1989, Miller, Mangan, Pollard, Thompson, Felzer, and Magee 2005). This remains a contentious hypothesis that requires far more evidence than is currently available.

In addition to exerting their control over the land through the use of fire and over certain animals and plants, the post-LGM Aboriginal population in some locales dug channels and weirs for trapping fish and eels. These land management practices indicate not only a deep knowledge of the local environment but also, contrary to what the early British settlers thought, a strong commitment to particular parcels of land. While Aboriginal people did not have large food surpluses because of a lack of domesticable plants and animals that would have allowed them to build permanent towns and cities, they did not simply live in a state of nature. Each community owned the rights to use parcels of land and their resources and managed those parcels with complex strategies of burning, planting, animal transfers, and animal management.